The overall objective is to continue to investigate the role of lipids, proteins and lipid-protein complexes of the sarcoplasmic reticulum in the functional activities of these membranes and to initiate similar studies on adipocyte plasma membranes. Specifically, the following problems will be undertaken: (1) The sensitivity of the purified sarcoplasmic reticulum (Ca ions plus Mg ions)-ATPase to the addition and subtraction of small quantities of phospholipid will be used to explore the role of phospholipids in this membrane function. Detailed kinetic analyses will be done on purified ATPase containing varying amounts of phospholipid. The specific nature of lipid required to promote this ATPase will be explored and spatial probes will be used to define the interactions between the ATPase and lipid. (2) We intend to continue our search for an appropriate labelling agent or agents to localize phospholipid classes in the sarcoplasmic reticulum membranes. (3) Work on the subunit structure of the sarcoplasmic reticulum (Ca ions plus Mg ions)- ATPase will be carried out. (4) Our research on the sarcoplasmic reticulum membranes was initiated primarily to gain through the exploration of this relatively simple membrane the knowledge to ultimately explore the complex membrane systems importantly involved in metabolic regulation. To this end, work will be initiated on the metabolically important adipocyte plasma membrane. BIBLIOGRAPHIC REFERENCES: Bertrand, H.A., Yu, B.P. Masoro, E.J. The effect of rat age on the composition and functional activities of skeletal muscle sarcoplasmic reticulum membrane preparations. Mech. Ageing and Devel. 4:7-17, 1975. Yu, B.P. and Masoro, E.J. Localization of sarcoplasmic reticulum (SR) proteins. Fed. Proc. 34:468, 1975.